The present invention relates to processes for authenticating objects, ink sets and ink compositions used in such processes, and objects formed using such ink sets and ink compositions. The present invention also relates to an ink which can be used for labeling an object (for example, a document or other object) with identifying markings which can be rapidly verified as authentic and which are highly resistant to counterfeiting. In particular, the present invention relates to inks, for security documents, which can be used with low cost and available (xe2x80x9coff-the-shelfxe2x80x9d) technology for hardware, for verifying authenticity, and to methods of printing using such inks and methods of verifying authentication of objects containing markings of such inks.
Widespread availability of inexpensive document scanners and color inkjet printers has created a severe problem, in that they have facilitated the creation of counterfeit documents in areas ranging from financial papers, access control documents, official identification documents, trademarked consumer goods, industrial component certifications, currency and entertainment event tickets.
Traditional government and corporate anti-counterfeiting technology has utilized techniques for discouraging copying based on restricting access to crucial raw materials such as special papers or inks, and by using printing techniques that require machines so costly that few can afford to acquire the necessary printing hardware. Such techniques include use of optical variable devices, such as holograms, embossed diffraction gratings, thin film interference coatings, laser images, etc.; special inks including ultraviolet, fluorescent, infrared, liquid crystal, magnetic, photochromic, thermochromic, optically variable, metallic and thermochromic color shifting inks, etc.; special substrates such as security papers, metallic threads, watermarks, embedded security strips, etc.; and exotic printing techniques such as laser engraving, intaglio printing, microprinting, continuous color shift printing, spatially periodic printed structures, see-through patterns (dual-sided printing), screen-angle modulation for periodic structure, etc. The intent behind these methods is to make the replication of the original document impossible without access to highly expensive printing hardware, or the authorization to purchase restricted raw materials such as special papers and inks. Most of these security labeling techniques rely upon the appearance of the object viewer whose visual examination of the object is the criterian used for its acceptance as a legitimate document.
These techniques are currently being compromised due to the availability of low-cost sophisticated color printers, image scanners and image processing software designed for use with personal computers. In addition, increasing sophistication in the commercial graphics arts fields has resulted in techniques used to produce objects such as embossed holograms, kinetigrams and diffractive color changing objects becoming public knowledge. Counterfeit credit cards and software certification labels having forged holograms have already been produced. Formerly exotic printing materials such as color-changing paint are being introduced commercially into areas as mundane as automotive painting. Human-verified visual security features in general are being rendered less effective with time, by the increasing ability to utilize commercial and consumer quality graphics hardware to make reproductions that while often not identical are rendered close enough to the original to pass a retail transaction inspection. Another reason for the failure of certain economic denial-of-resources based anti-counterfeiting technologies is that the profits in some areas of brand-named goods forgery is lucrative enough for counterfeiters to justify matching the expenditures of the legitimate printer of anti-counterfeiting labels. Another disadvantage is that these techniques of combating counterfeiting tend to restrict the printing of secure documents to those printed by large governments and wealthy corporations.
One attempt to counter this trend has been to introduce machine-readable security features into the protected documents. Some of the techniques include embedded magnetic strips, magnetic inks, periodic printed patterns that produce a Moirxc3xa8 pattern when viewed by electronic vision equipment, and recently data embedded in high resolution embossed patterns similar in format to CDROMs.
However, magnetic strips have been shown to be vulnerable to forgery with low-cost hardware. Embedded silicon chips are not physically useable for most paper-based documents. Optical card technology is suitable for mechanically stiff protected objects such as credit cards that can be fed into appropriate readers, but like smart chips is not physically compatible with the majority of documents requiring forgery protection. Printed bar codes are vulnerable to being duplicated by inkjet printers.
U.S. Pat. No. 3,928,226 to McDonough, et al. discloses an ink composition which can be provided for machine-readable tickets, tags, labels, postal imprints and the like, having (1) a visible color, that is, a color under ordinary mixed light frequencies, and (2) a fluorescent radiation color which, when irradiated with. ultraviolet life, for example, fluoresces preferably in the red wavelength of about 5800 xc3x85 to 6200 xc3x85. The ink imprint may be read visually and then read by a fluorescent machine reader which is set to pick up the fluorescent wavelength of the ink. Thus, this technique checks two different properties of a same ink.
U.S. Pat. No. 5,289,527 to Ligas, et al. discloses a method for authenticating articles, using a mixture of at least two photochromic compounds, the activated spectra having different absorption maxima. This patent discloses that by using combinations of photochromic compounds having instrumentally identifiable different activated spectra and preferably also other identifiable different photochromic properties, a verifying instrument can be used to identify the individual photochromic compounds used in the display data and thereby authenticate the article. This patent also discloses that basing authentication on different activated spectra and other defined characteristic photochromic properties of at least two photochromic compounds enables a large number of combinations and permutations which may be used to authenticate an article, increasing substantially the difficulty of copying the total system and thereby facilitating identification of counterfeit articles.
When using a mixture of coloring agents (for example, a mixture of dyes or a mixture of pigments), in one instance the spectral responses of the mixture of components containing the plurality of pigments and/or dyes are linearly additive (e.g., linear mixing of the spectra, or linearly additively combining of the spectral responses). This can be seen in FIGS. 1a-1c. Using fluorescence as an example, suppose that as shown in FIG. 1a a first pigment gives the fluorescent spectrum 1, and a second pigment gives the fluorescent spectrum 3 shown in FIG. 1b. If there is one-half as much of the first pigment as compared to the second pigment in a mixture formed from the first and second pigments, then the total fluorescent spectrum of the mixture will be that shown in FIG. 1c, having intensities 5 and 7, where the spectral response of the mixture is a linearly additive combining of the spectral responses of each pigment. If there is one-tenth as much of the first pigment as compared to the second pigment in the mixture, then such mixture will have a total fluorescent spectrum as shown in FIG. 1d with intensity maxima 9 and 11, where the spectra of the two pigments are linearly additive.
Linear mixing can provide a great variety of spectral patterns; however, where a well-equipped and determined counterfeiter has acquired knowledge of the set of inks used on a particular document, and also has a reader for reading such documents, by measuring the spectrum of a marking (e.g., dot) and knowing the set of inks used to print the marking the counterfeiter in a few trials can determine the mix the pigments used to make the marking and can reproduce the desired spectrum of the marking, and can thereby provide what appears to be an authentic document which in fact is a counterfeit. While, with many markings using different mixtures of inks, it becomes a tedious task to determine the compositions of the markings, if the set of inks used on a particular document is known such task becomes much easier using a computer. For example, a counterfeiter could use the reader to obtain separate spectra of each ink component, and then use equations of linear mixing in a computer to determine the linearly mixed ink composition of each marking. While use of special, secure ink sets will greatly inhibit the ability to provide a counterfeit, such special, secure ink sets are usually expensive, detracting from linear mixing as a technique for avoiding counterfeiting. Moreover, limited distribution ink sets as an anti-counterfeiting measure is also vulnerable to compromise by theft and unauthorized sales, and diversion or theft of such ink sets can potentially compromise thousands of protected items.
Accordingly, it is still desired to provide a technique for providing a secure object (e.g., document) and for verifying authenticity of the object, which is highly resistant to counterfeiting and which can use inexpensive and plentiful hardware components, and which provides rapid verification of authenticity. It is desired to provide such technique highly resistant to counterfeiting, notwithstanding the present day use of basic inkjet, imaging and computer image processing technology which have facilitated the creation of counterfeit documents.
The foregoing needs are satisfied through use of the technique of non-linearity of spectral response in the at least one marking checked for authenticity. That is, the marking has a spectral response which deviates from a predicted linearly additive spectral response, the prediction being formed by adding the spectral responses of the ink components which form the ink composition making the marking. Through use of the non-linearity (also described herein as xe2x80x9cnonadditivexe2x80x9d color combining or mixing), a xe2x80x9ctrap-doorxe2x80x9d printing function can be used in order to hinder a counterfeiter. Thus, a xe2x80x9ctrap-doorxe2x80x9d printing function (one in which it is easy and cheap to print a, e.g., security label, but in which the printing technology makes it hard and expensive to figure out how to duplicate it) is implemented for the purposes of the present invention. Because of the difficulty of determining the proportions of each ink component used to form the ink making each dot (due, e.g., to the non-linearity of the spectral response of the ink making each dot, relative to spectral responses of these ink components), from the dot itself, a counterfeiter has to expend orders of magnitude more effort to duplicate the label than does the legitimate printer, rather than having to merely match the resources of the person printing the original label. That is, due to, e.g., non-linear (nonadditive) combining of spectral responses (for example, reflectance, fluorescence or absorption) of ink components forming the ink mixture of the marking, it becomes much more difficult to reverse engineer the printing ink composition of the marking, thereby hindering the counterfeiter. This is true even if the set of inks, forming the ink composition which made the marking, was known by the counterfeiter.
Thus, according to the present invention, security is implemented not by making critical components expensive or available only through restricted channels, but by securing a data key which contains the information about which inks were used to form each of the markings and in what proportion they were mixed for each marking; the basis to avoid counterfeiting is not expensive and restricted, e.g., inks, substrates, etc., but rather is a data key which indicates the ink components, and it is much more feasible keeping the data, key from a counterfeiter. The data key is the information necessary to reproduce the original security label. For security labels where the ink mixtures for each dot are determined by hardware random number generators, this data key may consist of a multimegabyte data file containing the mixture ratios for each individual dot giving each ink color used and in what proportions for that particular security label. Alternately, the data key for the same size array could be a password or pass phase for a security label with mixture ratios determined by a seeded software-based, random number generator. Thus, the present invention is usable in connection with low security documents and can be effective in high security applications, with printing/verification being achieved using ordinary and low cost hardware and ink components.
Non-linear mixing or combining of pigment spectra, or a spectral response of a mixture which deviates from a predicted linearly additive spectral response of the individual spectral responses of the components of the mixture, is a known phenomenon. Such non-linear mixing can be shown in connection with FIGS. 2a-2c. Suppose a first pigment, when used by itself, has the fluorescent spectrum shown in FIG. 2a, with intensity maxima at curves 21 and 23. Suppose another ink in a set contains a second pigment, that is itself not fluorescent but which changes the spectra of pigment 1; for example, 0.01 parts of the second pigment when mixed with the first pigment changes the spectrum of the first pigment as shown in FIG. 2b, having intensity maxima of curves 17 and 19. That is, the part of the first pigment spectrum 21 in wavelength segment 2 (350-400 nm) is not effected by the presence of the second pigment, but the 0.01 part of the second pigment reduces by 80% the strength of the spectrum of the first pigment that lies in the 5-8 wavelength segments (curve 19). A counterfeiter who has a reader and who has the ink containing the first pigment and the ink containing the second pigment will still have to carry out a large number of trials in order to find the mixture that produces the spectrum in FIG. 2b. Particularly where there is very little material in the marking (for example, a microdot is used), quantitative analysis of the molecular composition is very difficult and difficulties of the counterfeiter increase many times when a plurality of different markings are used, having, for example, different amounts of the second pigment mixed with the first pigment.
Moreover, this difficulty would further increase where there are more than two inks in the set of inks. For example, suppose a third ink contained a third pigment, not in itself fluorescent but capable of enhancing the strength of the short wavelength part of the spectrum of the first pigment. Then the mixture of the three pigments would produce the spectrum in FIG. 2c, including increased intensity as shown by curve 22. This, of course, adds immensely to the difficulty of counterfeiting a pattern.
Thus, utilizing desired sets of inks, resistance to counterfeiting greatly increases.
Specifically, as one aspect of the present invention, the present invention provides a set of ink components for providing ink compositions to form markings of an object, the set including a plurality of different ink components having respective spectral responses, whereby at least two of the different ink components can be mixed together to provide an ink composition, such ink components, when mixed together, providing a spectral response of the mixture which deviates from a predicted spectral response when linearly additively combining the respective spectral responses of the at least two of the different ink components.
As another aspect of the present invention, there is an ink composition comprising a mixture of at least two ink components having respective spectral responses, wherein the spectral response of the mixture deviates from a predicted spectral response when linearly additively combining the respective spectral responses of the ink components of the mixture. While each of the two ink components can have a color, it is also possible that at least one of the ink components does not have a color by itself, but affects the spectral response of another ink component when the components are mixed.
According to another aspect of the present invention, the ink composition can be applied to an object, whereby authenticity of the object can be determined. The object can include a plurality of the markings, and each marking can be a microdot, in order to increase difficulty of counterfeiting the markings (i.e., the object). Desirably, each of the markings is a microdot, and each microdot preferably can be substantially invisible to the human eye. Use of the marking as a microdot limits amount of material of the ink composition in the marking, further increasing difficulty in counterfeiting the marking (that is, increasing the difficulty in determining components of the ink forming the mark due to these being only a small amount of the ink).
As a further aspect of the present invention, the object can include two (or more) markings respectively of different inks having different spectral responses; and wherein at least one of the first and second spectral responses has an effect on the other such that spectral response of at least one of the first and second markings differs from the first or second spectral response of the respective inks. Again, due to such interaction it becomes more difficult to xe2x80x9creverse engineerxe2x80x9d the ink of the markings, and becomes more difficult to counterfeit the markings.
As another aspect of the present invention, the object includes a substrate with at least one marking thereon; and the ink of the marking interacts with the substrate such that the spectral response of the marking is different from the spectral response of the ink. Again, such interaction masks the ability to reverse engineer, and enhances difficulty of the counterfeiter.
Another aspect of the present invention is a printing method, wherein the ink composition is applied to a substrate, e.g., to form a marking on the substrate. Preferably, the ink composition is an inkjet composition, with the composition being applied to the substrate by an inkjet printer (e.g., a standard inkjet printer). Accordingly, convenient and inexpensive hardware can be utilized for forming the markings on the object, to provide an object which can easily be authenticated.
According to a further aspect of the present invention, the printing method further includes selecting at least two of the plurality of different ink components of the set of ink components as previously discussed, with a mixture of these ink components being applied to a substrate as a marking. Moreover, additional selections of at least two of the plurality of different ink components of the set can be performed, to provide markings (e.g., microdots) having different spectral responses, further complicating the ability to counterfeit the markings.
According to further aspects of the present invention, a matching template is made which indicates authentic markings on the substrate of the object; through use of such template, verification of authenticity of the markings on the object can easily and rapidly be performed.
The matching template is the information that exists on, e.g., a verification computer which is compared with the information measured from the, e.g., security label in question to determine whether the security label in question is genuine. Due to the nonadditive color mixing (non-linearly additive color combining), the matching template cannot practically be determined calculationally from the data key, but can be generated by printing and then taking measurements of the resultant printed security label. Conversely due to the nonadditive color mixing, the data key cannot be derived computationally given the matching template. This is the essence of the one-way function. Such one-way function is particularly effective where the nonadditive color mixing is strong.
The original printer prints the label using the mixtures at each point as defined by the printer""s personal data key and then takes multispectral measurements of the label to make the matching template for that label. Anyone with the printing hardware and the data key can generate a matching template at will by printing out a label using the data key to define the mixtures and then taking measurements of the spectral characteristics of the resultant printed security label. If one possesses only the printed label without possessing the data key one is always free to make a matching template; however, one cannot replicate the label since that would require obtaining the data key or its equivalent from the matching template, which with a properly designed inkset and printer should be an intractably hard task.
The matching template for the purpose of this invention is a multi-spectral contour map made from the measured relative intensities of each area of the security array at each characterized wavelength. For a microdot-based array this is the contour map made from the measured relative intensity at each wavelength of each microdot relative to its neighbors. The matching template is desirably stored as an array of numbers on the computer or computers used to verify the legitimacy of the security label in question. If the nonlinearly additive color mixing is strong and the resultant spectra complex, the matching templates for legitimate security label protected items can be made public without compromising the protected item.
Furthermore, the method of the present invention lends itself to implementation via computer, computer-controlled inkjet printers and computer networking technology. That is, the template can be stored as an intensity contour in a computer, and measurements of markings on an object can be compared thereto to determine authenticity. The matching template can be stored at a remote server, with measured (tested) objects at a distant location having the measurements sent, for example, over the Internet, for comparison with the matching template at the remote server.
According to another aspect of the present invention, coloring material is applied to a substrate, and such coloring material is selectively reacted so as to change the spectral response of reacted portions thereof. Again, due to difficulty in reverse engineering the spectral response of reacted portions, difficulty in counterfeiting is enhanced.
The present invention has many uses, both in connection with high-security and low-cost implementation. For example, the present invention can be used in general for document security, counterfeit detection and physical access control (for example, in optical card keys). Various specific uses include trademark and label verification, use directly as an optical card key, credit card protection, identification badge security, passport and visa verification, check verification, and identification document (e.g., birth certificate and immigration card) authentication. The present invention can be utilized on ownership or title documents in order to verify authenticity thereof (prevent counterfeiting), and can be utilized for protecting brand name goods and labeling semiconductor chips. The present invention can also be used for verifying music and video CDs, verifying software source disks and verifying drug prescriptions. The present invention can also be used for providing password control for high value software, authenticating collectibles, providing protection for entertainment and event tickets and guarding against forged parts certification. The present invention can also be utilized for providing counterfeit-resistance tags for legal and financial documents. The present invention can provide tamper resistant seals and labeling, and can also be utilized for providing postage stamps.
Thus, the present invention moves in a different direction for combating the counterfeiter. It does not rely upon denial of access to sophisticated and expensive hardware, but relies upon methods more akin to cryptography, with the ability to reproduce a security tag being dependent upon possession of a piece of information similar to a cryptographic key rather than the exclusive possession of certain pieces of hardware. Without possession of the specific information key, even if the counterfeiter is in possession of the original printed object and printing hardware used to create it, counterfeiting can not easily be achieved.
Accordingly, the present invention enables a security printing technique to be achieved without the need for sophisticated printing hardware or restricted access materials. The use of this technique for the present invention is not dependent upon a person""s ability to purchase expensive hardware or control distribution of restricted access raw materials, and potentially enables low-cost consumer-grade computer hardware to be used to print secure documents. The present invention is more resistant to being compromised by thefts of raw materials or from attacks by a well-financed counterfeiter.
The printers and readers used in the present invention can be provided by applying available technology for some custom modifications of xe2x80x9coff the shelfxe2x80x9d items. The printers used in the present invention, for example and not to be limiting, have firmware modifications to allow them to be commanded to print ink dots directly on top of previously printed ink dots. Since current printers print complex colors by printing a multi-color mosaic of individual primary colors, xe2x80x9coff the shelfxe2x80x9d printers will require an internal operating code modification to print dots on top of each other. The readers can be assembled using xe2x80x9coff the shelfxe2x80x9d components and some custom software.
Moreover, the present invention can be used in combination with conventional security printing methods, to provide an even further enhanced security and confidence level in avoiding counterfeiting. For instance, the use of restricted-access, custom inks, non-commercially available ultra-high resolution print heads, and non-standard wavelength verification, and the use of print heads which print with much larger numbers of different ink types than commercial print heads, are examples of augmenting the present invention with conventional security printing techniques.
A further advantage according to the present invention is that it becomes economically practical to print and have archived unique security labels for each individual item to be protected. This is in contrast to documents protected by conventional security labels such as holograms, where a single successful forgery can be used to compromise thousands of protected documents.
The potentially very low cost of the optical reader, combined with verification of patterns over the Internet, can allow the average consumer or employer to check the authenticity of brand name goods, collectibles and legal documents (for example, checks, diplomas, and immigration work permits).
Moreover, counterfeiting by label transfer has been used as a method of defeating optical variable device-based (for example, hologram-based) security labeling. The ability of inkjet techniques to be used according to the present invention, to allow direct printing of the security pattern onto the item to be protected, allows industrial parts, electronic chips and construction materials to have greater protection against substitution by a counterfeiter of substandard parts.
The technique of the present invention can be readily scaled for use in both low and high security applications. For example, amusement park ride tickets might be printed with an identical low density dot pattern verified at only one wavelength by readers having the matching pattern stored locally in its own memory. Diplomatic passports might have security labels which utilize proprietary inks, have million drop arrays printed with nonstandard ultra-high resolution print heads, have imaging done at multiple wavelengths including in the infrared and ultraviolet, and require confirmation by multiple remote servers, providing a very high level of security. Thus, the present invention has the additional advantage of great flexibility in its application.